Disturbing knocking sound on first startup
 

I started my engine for the first time after finally getting it installed. After a few ignition and fuel supply issues that I got sorted out it fired up and ran. After reving it up to 2000rpm to start the break in procedure, I noticed a bit of a knock, knock, knock that I isolated to the right side of the engine. It pretty much went away below 1000rpm, but got louder with higher RPM's. It didn't sound like anything catastrophic and did not change in pitch over time. I ran it for ~10 min then shut it down and drained the oil. My first thought was a tight valve that might be kissing the piston, so I took off the valve covers and checked all the valves. All were in spec except for cylinder 5 which were a bit tight. But as I was adjusting them, I noticed that I was able to depress the #5 valves (i.e. compress the springs) easier than all the other ones, both exhaust and intake. I've been scratching my head for awhile on this one. I had a well respected Porsche machinist do the heads for me, so they were fully assembled when I got them, but I don't remember specifically testing how hard it was to depress each valve before installing them.

Does anyone know why these two valves might depress easier than all the other ones? I just checked and it was cylinder #5 that was the bad one when I rebuilt it (severely scored piston/cylinder). While all pistons/cylinders were replaced, is it possible that the valve springs were on that cylinder were compromised? I will check with the machinist whether he would have checked each spring prior to reassembly.

Any other ideas?

Thanks.

Geoff

Did you prime the oil system before starting the engine? You should turn the engine over on the starter with the distributor wire grounded until the oil pressure comes up on the gauge.

Yep, well primed prior to start-up and good oil pressure.

Geoff

Are you saying you can depress that #5 valve with your fingers, or it feels weaker when using the screw adjuster to move it? You should definately not be able to move the valve with your fingers, even if you are Lou Ferrigno.

I can not depress it all the way, of course, but I can lift it off the seat by pushing down on the rocker arm. I can lift all of them off the seat a tad, but #5 seems to be easier and I can push it down farther (I'm only talking 1mm or two). They are not floppy and they do require some force to lift them, but not excessive force. I don't think I have bionic fingers. Is it possible that all my springs are weak?

Thanks.

Geoff

I'll need to defer to more experienced builders here. I'm no weakling, rockclimbing keeps your hands pretty strong, but all the heads I've had built or built myself were very stiff. I couldnt move them.

I agree, something sounds strange there. If I were you I wouldn't run the motor again until you have spoken with the machinist who assembled the heads. Rather then being your technical problem to solve, it should be his customer service problem to solve.

By the way, did you check all of the valve clearance when you put the heads back on?

broken valve spring?
did he put both springs back on or just one?

The good news is there is a Porsche tool that will let you remove the valve springs in the car. My guess is you have a bad spring. It's easy enough to pull the spring and test it. (or replace it with a pair of new springs and try it again)

Pictures would be helpful but it sounds like something is funky with your valve spring assembly. As said above the springs are pretty stout but if one of the two or both are broken or are the incorrect part then that may be where the problem lies. There are other pieces in the system that may warrent further inspection as well. There are "rings" and "washers" (read - spacers) that are used to set the valve spring height. If the springs are ok it is possible that these may be missing or assembled incorrectly. In effect there would be very little to no preload on the spring which may explain why you can depress the spring with hand pressure.

From the sounds of it this would explain your mysterious knock very well. With little or insufficient spring pressure your engine was probably experiencing valve float. At low rpms the spring pressure was sufficient to keep the valve "on the cam". At higher rpms the valve may have "floated" in which you may just have heard the slapping of the valve. In a worst case scenario the valve may have contacted the piston dome. Stock SC cams are pretty mild so hopefully there was no piston/valve impacts.

Depending on what you find out with regards to what was wrong with #5, I would recommend checking the other valves/springs pretty closely before butting everything back up.

Thanks all for your input and comments. I've checked with the machinist who worked on the heads and he verified that he would have checked the springs. Although I would have sent him the springs and valve parts in zip-lock bags (one for each cylinder), he indicate that he would not have kept them separate, so it is unlikely that springs/valves initial on the failed cylinder #5 would have landed back on that cylinder. I do not want to mention the machinist's name here as he is a very well respected machinist in the Porsche community and I don't intimate that this problem may have been caused by him in any way. If he said he checked the springs, I believe him. That said, I'm not sure why the valves from just one cylinder would depress that much easier than the others.

While valve noise is typically a ticking, I think that is usually due to the contact made b/w the rocker and valve when the gap is not set appropriately. Knocking usually means connecting rod/piston sort of issues, but as Fast Corners says a floating valve due to a weak/broken spring might make contact with the piston head and sound more like a knock.

I didn't realize that there was a tool to remove the valve spring w/o removing the head. I will likely pull the engine out of the car anyway as its easier to work on. The hour I spend pulling it out/putting it back in will be worth it so I can see things easier.

Does anyone else have any input on how hard it is to push down a valve? As I say, with a bit of thumb pressure on the rocker arm, I can lift all the valves off their seats - #5 valves just seem to be easier to lift and I can push them a bit further.

Thanks again.

Geoff

Oh, and yes, I did check all the piston/valve clearances as per Wayne's book during the reassembly. Knowing this was a critical step, I checked, double and triple checked them.

Geoff

I appreciate your respect for the machinist. But since I work in the sales/customer service world in my day job, let's walk through the scenarios...

1) You take the appropriate parts off the engine apart and conclusively determine that there is a valve spring which is broken/missing/not set correctly. Since the heads were delivered assembled, the situation is that the "respected" machinist comes off as being something less then respectable. You've spent a bunch of time tracking down that he didn't do something that he should and now you're pi$$ed off and start telling your friends. The end result is that you're frustrated, out the dollars for the special tool and the well known machinist's reputation is damaged.

2) He takes the initiative to help you track down and fix the problem. Now he's part of the solution rather then the problem. He can help you quickly get the car back on the road and has the opportunity to make things right with you. You get your car back on the road and happily tell everyone how great the machinist was in helping to solve the problem, which may not have even been his problem. Now his reputation moves up a notch.

Admittedly, people don't always appreciate the opportunities for strategic customer service which are in front of them. Sometimes, as customers it's up to us to gently point these people in the right direction and help them to "do the right thing" before they inadvertently make things worse.

BTW - Is this machinist within driving distance of you?

John,

I plan to tear it down this weekend and see if I can locate the issue. I have no doubt that he will help me determine the problem and work with me to fix it, even if it is not a problem that is associated with the work he did on the heads. I've already been in communication with him regarding this.

To be honest, this is not a huge inconvenience for me. I was actually dreading having to start into working on the interior of the car now that everything else is done. I'm actually looking fwd to tearing that side of the engine down this weekend to understand the problem - there's always that great satisfaction when you identify and correct a problem.

(Can anybody tell that I'm Canadian?)

Thanks.

Geoff

FWIW ... I looked at your rebuild blog.

Nice work. Your engine looks beautiful. Best luck sorting it out.

How are we supposed to know that you're Canadian without any references to beer -- eh??

Where are you in MA?

John,

I'm in Millbury (near Worcester).

mca: Although its very hard to hear in the video of your rebuilt engine being broken in, I hear indications of the noises I heard in mine that concerned me. Maybe I'm being over cautious here. I heard a bit of a high pitched "tinging" that bothered me. Maybe I've thrown you all off by characterizing it as a "knocking."

Part of the problem is, and I know you will all find this very strange, I have never really heard what a 911 engine is *supposed* to sound like. Sure, I've heard a 911 whiz by me now and then, but this is my first 911. When I bought it, the engine was sitting in a snowbank beside the car (PO couldn't afford the rebuild the mechanic told him it needed and the mechanic wouldn't put the engine back in the car). That said, I have plenty of experience rebuilding motorcycle engines. I was actually impressed by the throatyness of the engine sound when I first started it up. It was only after I was listening to it closely after it had been running for a few minutes that I noticed this "tinging" coming from the right side of the engine. It is possible it is benign, but I would prefer to get to the bottom of it as I see no reason why the right side of the engine should not be as quiet as the left side.

When I took the valve covers off lastnight and re-checked the valve/rocker clearances I noticed that cyl #5 was a bit tight and it seemed to be easier to push those valves down. So, I want to pull the engine out and try to do a better assessment of this.

One more thing - I'm using the 964 grind for my cams (I think they have a bit higher valve lift).

Geoff

If you are talking about the noise at idle, that is more or less the raspy sound of the exhaust.

Believe me ... I am SUPER paranoid about my engine. I had the local pros check it out a few times just to make sure everything was sorted out.

Maybe you could start it up and have your local mechanic listen before you tear it down again. They have great ears!

Ok, I think I've found the problem.

Just so you all don't think I'm crazy, here's a video showing how easy it is to push the #5 exhaust valve open. The #5 intake is the same.

I also looked down the valve springs on all the exhaust valves and noticed that I can see the valve spring seats at the bottom of the other valves, but can't see one on the #5 exhaust valve. The valve seats are the cad-plated yellow color which makes them easy to spot against the aluminum. On the #5 valve, tho, I can just see the aluminum seat the valve spring assy sits in.

A valve without a seat would explain why its so easy to depress and would likely float to kiss the piston (hopefully a very tender, gentle kiss).

Does anyone in MA have the intake and exhaust valve spring compressor tools I could borrow?

Thanks.

Geoff

Hopefully you got lucky and the rattling noise you heard was just the spring rattling around and not piston/valve contact. You might be able to look down the spark plug hole and see.

I've got a c-clamp style valve spring compressor if you're interested. I just PM'd you. Let me know.

John, thanks for the offer, but I've got one of those as well. I contacted the machinist who did my heads last night and he's going to send me the tools that allow engine-in-car valve spring removal.

Geoff

Do a leakdown test on #5 to see if the valve is bent. That would influence the decision to tear it down or not.

Good idea.

Geoff

How did this workout? Did you confirm the valve spring seat was missing?

The tools to do the in-car removal the valve springs should arrive in the next few days. I'll let you know when I get the springs out.

Geoff

Geoff,
If you can depress a stock valve spring on an assembled Porsche engine with your hand (no mechanical advantage levers, etc.) ...

Remind me to never shake hands with you!

The book says that it takes 95 lbs to move the valve off the seat (seat pressure) !

You are The Man.

Mark

I see a problem with your video that shows pushing the valves with your thumb. Remember that a spring force increases as it is compressed. The #5 valve is easy to press because you are pressing it at its lowest load when the valve is seated. This is simply the preload setting which should be found in the factory spec book for the car. The other valve (#4 I think) that you could not move was way compressed so the force would have been much greater from the spring. Not to say you still don't have problems, but find out what the spring seat force from the manual should be and that will give you an idea how much force you should push with your thumb to move that #5 valve .
Now the only guy that can move springs with his finger is Chuck Norris according to the lists I have seen on him......joking.
Good luck.

As a further check, rotate the engine to get the #4 valve seated or TDC on number 4 and then press it. If the force to move it 1mm is the same then #5 is no different than than the others and it may be something else.
Just a thought.
Also ask the rebuilder what the spring seat pressures and spring heights he set everything to were. This confirms he actually checked and installed them properly. Someone before mentioned 95lbs. don't know if this is right though.

Yes, in the video I did try to move #4 and #6 as you indicate, and that's not really valid as the valve springs may already be partially loaded by the cam. But, I did check each valve spring's pressure with each piston at its TDC. I can depress all the valves with very similar force except for those on #5 which are much easier.

Geoff

Ok, so I rec'd the tools and additional valve spring seats/shims from my machinist to allow me to do in-car removal of the springs. I just removed the #5 exhaust valve spring and, as I suspected, there was no spring seat. So, what do I do now?! How do you properly shim a valve spring? I have a handful of shims, but how many do I put on? Do you typically use some sort of load cell to measure spring rate, adjusting with shims as necessary? Or, do you measure the spring height and adjust with shims to some tolerance?

Thanks.

Geoff

This is why one should always double check the work of others. That should have been easy to spot before assembly. Good lesson to learn. Sorry it had to be you. Mistakes happen, hope you get it sorted w/o damage to you engine.

The number I have for seat pressure is 75 lbs for a stock SC. There are numbers for the spring height but since you have 5 others to look at you could just measure one of them and match it.

my book has the following numbers for installed height of valve springs for 78-80 SC:

intake and exhaust 1.35-1.37 inches (34.2-34.8 mm)


-Andy

Carefully install a spring seat, spring retainer and locks, but w/o the spring. Using a vernier caliper, measure the distance between the seat and the bottom of the retainer. That distance is the installed height. Adjust the spring seat thickness to meet specs.

S

I am using a 964 grind cam on my SC. Since this has a higher valve lift, should the installed spring height be modified? If so, does anyone have these values?

Thanks.

Geoff

Valve lift determines how far the retainer moves toward the head. Thus, when setting up valve spring height, there must be adequate clearance so the valve spring doesn't stack (close up completely) nor allow the valve lock to contact the top of the valve guide.

To measure if there's adequate clearance, assemble a valve seat, valve spring and retainer assy. in a a bench vise and compress to the specified installed height. Mount a dial indicator to measure further jaw travel, then compress the assy. the amount of valve lift and see where everything ends up.

Are the valve spring coils almost touching. There's a min. suggested clearance.

This compressed distance between valve seat and bottom of the retainer should be more than the distance the valve guide projects from the head.

You might have to look up the exact numbers somewhere or maybe Steve or Henry or ?? can suggest those values.

Something like that.

Sherwood

Sherwood: Ok, I got the proper installed spring height and procedure to measure this. Once I get the springs in and properly shimmed on #5, I will be able to compare how easy it is to lift those valves versus the others and determine if I need to pull all the valves out to check.

Geoff

Since you found this error with one valve why not remove the engine and recheck all of them to be sure they are correct? Get the specs on spring seat pressure and installed height and get them all to spec.
You will likely feel better doing it this way as you put another 150k miles on the engine before the next rebuild.
Peace of mind is worth alot.

I pulled the engine out of the car and installed the intake valve shimmed to the proper height and, lo and behold, I cannot depress the valve with all my might. So, I removed the intake valve from #4 and found that it, too, did not have a valve spring seat. What I thought was the cad-yellow colored spring seats were actually shims. So, none of my valves have spring seats, it was just that #5 had no shims. Looks like I have my work cut out for me.

Geoff

...and a refund on the way I hope!